qdisc: add TCA_XSTATS stats for fq qdisc.

When using fq, we rely on xstats useful metrics to check fq behavior and
diangosis, it is what can be seen from iproute2 tools, `tc -s qdisc
show` as well. It exposes metrics as:

https://github.com/iproute2/iproute2/blob/main/include/uapi/linux/pkt_sched.h#L847

Signed-off-by: Kangjie Xu <[email protected]>

Author: Kangjie Xu

class_linux.go

@@ -398,3 +398,13 @@ func parseTcStats2(data []byte) (*ClassStatistics, error) {
 
 	return stats, nil
 }
+
+func parseTcFqXStats(data []byte) (*nl.TcFqQdStats, error) {
+	buf := &bytes.Buffer{}
+	buf.Write(data)
+	stats := &nl.TcFqQdStats{}
+	if err := binary.Read(buf, native, stats); err != nil {
+		return nil, err
+	}
+	return stats, nil
+}

qdisc.go

@@ -3,6 +3,8 @@ package netlink
 import (
 	"fmt"
 	"math"
+
+	"github.com/vishvananda/netlink/nl"
 )
 
 const (
@@ -308,6 +310,8 @@ type Fq struct {
 	LowRateThreshold  uint32
 	Horizon           uint32
 	HorizonDropPolicy uint8
+
+	Stats *nl.TcFqQdStats
 }
 
 func (fq *Fq) String() string {

qdisc_linux.go

@@ -488,6 +488,16 @@ func (h *Handle) QdiscList(link Link) ([]Qdisc, error) {
 					return nil, err
 				}
 				base.Statistics = (*QdiscStatistics)(s)
+			case nl.TCA_XSTATS:
+				switch qdisc.Type() {
+				case "fq":
+					fq := qdisc.(*Fq)
+					s, err := parseTcFqXStats(attr.Value)
+					if err != nil {
+						return nil, err
+					}
+					fq.Stats = s
+				}
 			}
 		}
 		*qdisc.Attrs() = base

qdisc_test.go

@@ -515,6 +515,10 @@ func TestFqHorizon(t *testing.T) {
 		t.Fatal("HorizonDropPolicy does not match")
 	}
 
+	if fq.Stats.GcFlows != 0 || fq.Stats.ThrottledFlows != 0 || fq.Stats.HorizonDrops != 0 {
+		t.Fatal("Stats is not zero")
+	}
+
 	if err := QdiscDel(qdisc); err != nil {
 		t.Fatal(err)
 	}